Wet sanding machine



. Nov. 12, 1940. w. L. GOODSTEIN WET SANDING MACHINE Filed June 16, 1938 2 Sheets-Sheet 1 NOV. 12, 1940. w, GOQDSTEIN 2,221,448

' wm' SANDING MACHINE Filed June 16, 1938 2 Sheets-Sheet 2 Mum/v L @mmem/ Patented Nov. 12, 1940 UNITED STATES PATENT OFFICE This invention relates tothe art of wet sanding, a term applied to the extremely delicate operation of sending ofi minute irregular high points on coatings ofpaint, lacquer, varnish or other similar materials applied to surfaces upon which a very fine finish is required, such as automobile bodies and the like. Such sanding operations require a sanding paper that is spe-- cially manufactured for the purpose, and a high degree of skill on the part of the operator. The surface operated upon is wet with water and is invariably composed of an extremely thin coating that is most highly susceptible to scarring and disfigurement. The applied pressure must be so light and so uniform over the surface operated upon that an operator must concentrate closely upon his work.

Thus, wet sanding differentiates sharply from all other types of. sanding or abrading operations where the primary purpose is to scour and grind down into the surface operated upon without regard to appearance of the finish; the concern being to the actual removal to a. definite depth of the material acted upon.

So exacting are the requirements for proper wet sanding that it has not heretofore been considered feasible to perform the operation other than manually by expert workers. The sanding paper must, so far as possible, be uniformly reciprocated in straight lines without lateral variation. The movement cannot be in an orbital stroke as the curved lines which result, although almost microscopic, cause light refraction and dull or otherwise impair the high finish which it is desired to produce on the surface being sanded.

Prior to the advent of this invention there has been no apparatus capable of wet sanding mechanically in a manner to meet the stringent requirements of the art. Sanding ma.- chines generally cannot be adapted to the purpose. They have too great a vibration and their supporting rollers are incapable of operating over a wet surface without slipping. They have no satisfactory means of controlling the pressure of the standing element, which pressure must be very delicately controlled in wet sanding. They have numerous other objections well recognlzed by those skilled in the art.

It is, therefore, an object of this invention to provide a. machine capable of wet sanding at an operating pressure of sanding element which is at all times under the control of an operator and which is instantly responsive to control variations of applied pressure.

Another object is to provide a. wet sanding machine having work engaging resilient supports capable of free sliding forward movement over a wet work surface and which are inhibited against lateral slipping or skldding thereon.

Still another object is to provide a wet sanding machine having resilient means manually compressible between the machine and its work whereby the applied operating pressure may be controlled to a high degree of sensitivity.

A still further object is to provide a wet sanding machine having work engaging resilient supports compressible between the machine and its work whereby to regulate the depth of a sanding operation, and in which one of the supports serves as a means for cleaning the sanded surface.

Other objects will be readily apparent to those skilled in the art.

This application is a continuation in part of my prior application Serial No. 146,234, filed June 3, 1937, for Sanding machine.

In wet sanding a treated-surface, such as, for example, the painted, lacquered, or otherwise coated surface of an automobile body, it has been universal practice among workmen to sand the surface by rubbing a piece of wet sand paper of special manufacture over a water wetted area. The sandpaper was held in the operators hand with the fingers behind the paper and pressing it against the surface to be sanded. Such practice frequently resulted in the appearance of finger marks or slightly grooved areas where the pressure of the fingers on the back of the sandpaper was somewhat greater than the pressure of the sandpaper between the fingers. In order to minimize such undesirable finger marking the operator would lean against the automobile body, near the surface being sanded, in such manner that the weight of his body would not be applied as a part of the pressure on the sandpaper. By thus leaning against the body of the automobile the operator was able to regulate the pressure in a more even and selective manner. In some cases the sandpaper would be backed by a block.

All such practice required that the sanding operation be carried out relatively slowlyas otherwise the sensitive touch by means of which the operator could vary his pressure would be lost. After sanding, the treated area was wiped clean and dry, and the operators position was then shifted for a. repetition of the sanding over a diffrent area.

The resultant break in continuity of sanding, many times repeated, not only increased labor time and therefore expense, but also adversely affected the result in that it was practically a physical impossibility for an operator to commence a subsequent sanding and maintain it at the same pressure as that applied in the immediately preceding operation.

It is, therefore, an additional object of the invention to provide a wet sanding machine that shall be commercially economical in that ing element.

it will permit faster sanding while at the same time enabling an operator to maintain the same sanding pressure over the entire area of the surface to be treated.

in the accompanying drawings, wherein like characters of reference designate like parts throughout the several views:

Figure 1 is a side elevation of a machine constructed in accordance with the invention and as operatively engaged against a surface to be wet sanded.

Figure 2 is a similar elevation of the 'machine, but as in a position of rest with the sanding element disengaged from the work.

Figure 3 is a perspective view of a novel form of sandpaper holder employed in the machine.

Figure i is a side elevation of the holder.-

Figure is a front end view of the machine.

Figure 6 is a rear end view thereof.

The present disclosure constitutes but one structural embodiment by which the invention is reduced to practice, and it is to be understood that the principles of my' invention are capable of expression in various other structural arrangemerits, the details of which may be varied as desired within the limits imposed by the scope of the invention as claimed.

The major features of the invention comprise a sanding element, mechanism for reciprocating the sanding element relative to a surface to-be treated, and compressible resilient supports for the mechanism extending therefrom normally in advance of the operating plane of the sand- The operating mechanism is fashioned in a manner to provide a convenient hand grip through which manual pressure is applied to compress the resilient supports and thus bring the sanding element into engagement with the work at an operating pressure constantly under control of the operator and instantly responsive to his regulation thereof. At the same time the supports preclude possibility of sidesway or skidding of the apparatus on the wet surface being treated while permitting free sliding thereof in the direction of its operating movement under guidance of the operator.

In the embodiment herein illustrated ,the operating mechanism of the machine comprises a pneumatic motor iii of the reciprocating piston type, whereof the cylinder by virtue of its contour conveniently provides a hand grip by which the machine may be applied to andv guided over its work, comprising a surface to be treated. The

motor is of a well known construction commonly employed for windshield wiping purposes and includes a flat rectangular base plate I! fixed with respect to the motor cylinder and appropriately slotted longitudinally to provide clearance for the operating play or stroke of an actuator arm l2 fixed to the piston (not shown) and reciprocable therewith through a wall of the cylinder. At one end the cylinder has an axially extending power supply nipple l3 threaded for coupling into a pressure supply control valve l4 associated with a main control valve I5 carrying a connecting nipple l6 for coupling to a flexible power supply conduit (not shown). The precise details of valve control and power supply, and type of motor whether hydraulic, suction, pneumatic or electric, are immaterial, and may obviously be as desired.

The sanding element comprises a rectangular backing block- W having a plane bottom face to overlie the work. A sheet or strip of the specially prepared wetted sandpaper i8 is Wrapped around the block with the two ends overlapped on the upper block face, and the unit thus assembled is detachably inserted upwardly within a holder l9 consisting of a fiat plate having parallel downturned end flanges 20. One end flange is apertured at spaced points to provide bearings for a pair of screw bolts 2| headed externally of the flange and whose stems are threaded at their inner 'ends into a clamp plate 22 slidable on the plate l9 and normally urged in the direction of the opposite end flange, which it parallels, by tension of expansion springs 23 coiled about the stems of the bolts and bearing at their ends against the opposed faces of the clamp plate and the adjacent end flange 20. When the sandpaper covered block is inserted in the holder the clamp plate 22 is forced against one end of the backing block in firm frictional holding engagement, the other end of the block being forced tightly against the adjacent end flange 20. The tension of the springs 23 is sufflcient to insure adequate clamping pressure by which the sandpaper covered block is held in proper position against slipping or dislodgment in its holder during operation of the machine. Figure 4 illustrates in dotted lines the mounted block and the range of movement of the clamp plate by which it is held.

The holder plate I9 -is backed by a second and smaller rectangular plate 24 riveted thereto and to which in turn are riveted a pair of longitudinally aligned stirrups 25 having parallel upturned arms 26 at their ends. The inner opposed end arms are arranged in spaced relation to receive therebetween the actuator arm [2 from the motor, as shown in Figures 1 and 2. A rod 21 is disposed transversely through apertures provided for the purpose in the arms 26 and through an accommodating slot provided in the actuator arm i2. Spacer sleeves 28 are mounted on the rod between the respective pairs of stirrup arms 26, and the outer ends of the rod extend laterally beyond the adjacent arms 26, being threaded to receive wing nuts 29.

It will beobvious that as the' wing nuts 29 are tightened the outermost stirrup arms 26 will be forced oppositely inward and Will impart a thrust to the spacer sleeves 28 which in turn will force the inner arms 26 toward each other to clamp firmly against the sides of the actuator arm l2, whereby the holder will be tightly secured on the actuator arm for reciprocation as .the motor is operated. The shank of the rod 2? bearing in the actuator arm slot provides an adjustable pivotal connection whereby the holder may be angled with respect to the actuator arm if desired and locked in its position of adjustment.

Also, the holder may be adjusted to the extent of the length of the slot in the actuator arm 12, whereby the holder may be moved toward or away from the motor, which also comprises the handle portion, and thus be adjustable to influence the sensitivity of the control of pressure on the sanding element, as will be explained.

At the front or leading end of the machine, considered with respect to the direction in which the machine is moved over a surface to be wet sanded, the motor base II has appropriately secured thereto at each side edge a depending finger 30 which at its lower end is rigidly secured to a transverse clamp bar 3| which cooperates with a second and similar transverse clamp bar 32, to secure therebetween the infolded and doubled portion of a wide, thick band of rubber or equivalent elastic material 33. At each end of the clamp bars, which extend outwardly beyond the side edges of the band 33, bolts 34 are provided by means of which the clamp may be operated. The band 33 is resilient as well as elastic, and its effective diameter is such that when the machine is rested idly upon a surface to be treated, indicated as at 35, a portion of the band will bear upwardly against the front end of the motor, as shown in Figure 2. to elevate the same at an angle sufficient to dispose the sanding element clear above the work surface 35. As more or less-of the band is doubled in between the clamp bars II and 32 the effective diameter of the band will be correspondingly shortened or increased,- and this adjustment provides a further means for regulating the sensitivity of the sanding pressure control.

The width of the rubber band 33 is greater than or equal to the width of the strip of sandpaper I8, and the band provides a wide, flat bearing surface that slides easily over the wet surface to be sanded. The band is held against perlpheral shiftingand thus, when pressed against a water wetted surface, it provides a suction grip thereon in the manner characteristic of rubber. In the direction of forward movement of the machine over its work the band slides easily as greater resistance is provided by the band as the area of resistance is then equal in length to the 40 full width of the band from one side to the other. This effectively serves to prevent sideskidding and confines the operating travel of the machine to a straight line, something exceedingly dlfllcult to accomplish in manual sanding. I

A squeegee 38, consisting of at least twopads of rubber, is detachably positioned in a socket 31 attached to the motor base II at the trailing end of the machine, and extends sufilciently far from the motor and perpendicular to the base II to project normally beyond the plane of the sanding element, as shown in Figure 2.

The sanding element is restrained against movement laterally of the base II by virtue of the engagement of its actuator arm I! between the arms 26, and as the rubber band 33 prevents sidewise movement of the machine it will be apparent that the direction of reciprocation of the sanding element is very accurately confined to a straight line.

go The band 33 and the squeegee at opposite ends of the machine provide resilient supports which extend normally beyond the operating plane of the sanding element, so that when the machine is initially applied to a surface to be sanded the 55 sanding element is disengaged therefrom until manual pressure is applied on the cylinder It in a direction to compress the resilient supports between the machine and its work. The resilient nature of the supports permits a wide range of sanding pressure control on the part of an operator, the sensitivity of which is enhanced by the relative adjustability of the band 33 and the sanding element on the actuator arm If.

The squeegee performs a double function of resilient support and wiper by which the sanded surface is immediately wiped clean following sanding so that the work may be constantly under unimpaired observation.

The presence of the compressible resilient supports, between which the sanding element recipa sanding element, base carried means for actuating said sanding element, a resilient work engageable support at one end of said base, a work engageable squeegee supporting the other end of said base, and said sanding element being operable between said resilient support and the squee- See.

2. A machine for sanding a painted surface, comprising a base to be pressed toward the surface to be sanded, a sheet of abrasive paper removably held in place on the base to engage the surface to be sanded, means for reciprocating the paper, stationary resilient means supporting one end of the machine as a whole and providing a resilient hand rest for the machine operator, and a relatively rigid but resilient squeegee supporting the other end of the machine from the painted surface.

3. A machine for sanding a painted surface on automobile bodies to establish a smooth surface,

comprising a movable holder carrying a sandingelement shaped according to the shape of the surface desired, a relatively longitudinal body constituting a reciprocating device for the holder, means connecting the holder to the device, a relatively resilient support at one end of the device to serve as a spacing support to rest against the painted surface and to vary the spacing between the holder and the painted surface, thereby to control the depth of the sanding action, and a relatively rigid squeegee element at the other end of the device to support it during operation and to wipe the surface after operation.

4. A wet sanding machine comprising a base having hand grip means thereon, a sanding element, means on the base for reciprocating said sanding element longitudinally of the base, a

wide and thick band of rubber fixedly secured to the leading end of said base on an axis transverse to the base to Provide a non-skid resilient supporting cushion therefor normally extending beyond the operating plane of the sanding element, and a squeegee supporting the other end of said base and normally extending beyond the operating plane of the sanding element.

5. A wet sanding machine comprising a base, a

of the band.

WILLIAM L. GOODSTEIN. 

